McCarthy was entering her vehicle in the parking lot of a Planet Fitness in New Hampshire at around 10 p.m. on June 12 after her shift was over. The footage shows a man getting out of his car and then punching McCarthy in the back of the head.

McCarthy said she was punched about 39 times and thrown to the ground. However, the surveillance footage stops after the first punch.

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"He just kind of came up and hit me in the back of the head and wouldn't stop," McCarthy told CBS News. "He didn't say a word and he didn't have a reason behind it. I asked, 'Why? Who are you?'''

The teenager believes the assailant could have been a disgruntled customer who had an issue with her, but she could not identify him. She did not suffer any serious injuries despite being punched several times.

"I just thought he was just coming in to work out. That's why when he walked right by me I didn't think to turn around or anything," McCarthy told NECN. "I didn't think anything weird of it.

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"I thought someone was just messing with me and I turned around laughing because I thought they just pushed me in the back of the head. But then I realized it wasn't joking and he continued to keep beating me.

"That was really disturbing. He didn't say a single word at all. He was silent through the whole thing."

Police are now looking to identify the man in the video. He is a described as a white male wearing a white T-shirt, shorts, white sneakers, baseball hat, and sunglasses. Authorities are looking for tips which may help identify the suspect.

Police believe the suspect fled in a light-colored Ford Fusion or similar-looking vehicle.

"Obviously he was trying to disguise himself to a point so that nobody could identify him," said Rochester Police Lt. Jeremy Aucoin.

Planet Fitness has issued a statement on the attack: "The safety and well-being of our members and employees is our top priority, and we are currently working with the local authorities in their investigation on this incident," the statement read. "We are committed to assisting however we can in their search and hope the suspect is apprehended quickly."